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i have to write a program that for 3 input numbers it decides if they can form a triangle and if is rectangle or not . I wrote

#include <stdio.h>
int main(){
    int a , b, c;
    scanf("%d %d %d" , &a , &b , &c);
    if ((a==2) || (b==3) || (c==4))
    printf("The numbers can form a triangle.\n");
    
    else if ((a==3) || (b==4) || (c==5))
    printf("The numbers can form an rectangular triangle.\n");
    
    
    else if((a==1) || (b==1) || (c==5))
    printf("The numbers can form a triangle\n.");
    
    return 0;
}


The program is printing me the first 2 printf , but for the third print it prints "The numbers can form an rectangular triangle"

What I have tried:

i tried separate by semicolons but not working
Posted
Updated 19-Nov-22 3:48am

Assuming that a,b,c are the length of the sides, then you have to use the triangle inequality (see Triangle inequality - Wikipedia[^]) in order to estblish if they form a triangle.
Similarly, you have a right triangle if
z^2 = x^2 + y^2
holds, where
z = max{a,b,c}

and {x,y} are the remaining lengths.
 
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Comments
merano99 19-Nov-22 8:13am    
+5
C++
if ((a==2) || (b==3) || (c==4))
printf("The numbers can form a triangle.\n");

In the above code if a equals 2 then you will print the message, regardless of the values of b and c. You need to test that all the values are equal, so it is a AND b AND c, thus:
C++
if ((a==2) && (b==3) && (c==4))
    printf("The numbers can form a triangle.\n");

You should als reduce larger values to see if they are in the same proportions as you are using here; for example [4, 6, 8], [12, 16, 20] etc.
 
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You implement here among other things constants, which can result in a rectangular triangle (Pythagorean theorem). However, the question refers to an arbitrary triangle. It is not clear how a rectangle is to result from the specification of 3 lengths. Is it possible that a rectangular triangle is meant here instead of a rectangle? From two equal rectangular triangles one could also build a rectangle.

As Palini had already suggested, for any triangle the triangle inequality would be usable and to check if it is additionally right-angled the Pythagorean theorem would be useful afterwards.

According to the triangle inequality, in a triangle the length of the longest side c must always be shorter than or equal to the sum of the sides a and b. This means formally:

c <= a + b

In a rectangular triangle, the sum of the areas of the cathetus squares must be equal to the area of the hypotenuse square. Here, a and b are the lengths of the sides adjacent to the right angle, the cathetes, and c is the length of the side opposite the right angle, the hypotenuse. This means formally:

c^2 = a^2 + b^2

The program design presented above should better use these formulas than statically evaluate the lengths.
 
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Quote:
The program is printing me the first 2 printf , but for the third print it prints "The numbers can form an rectangular triangle"

Because it is what( you requested.
Pay attention to the difference between '||' and "&&".
C++
if ((a==2) || (b==3) || (c==4))

With "||", test is true if 1 of the parts is true.
with "&&", test is true if all of the parts are true.
 
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